1. Field of the Invention
Exemplary aspects of the present invention relate to a curve correction mechanism, an optical scanner, and an image forming apparatus, and more particularly, to a curve correction mechanism for correcting a direction and degree of curvature of a reflecting mirror, an optical scanner including the curve correction mechanism, and an image foaming apparatus including the optical scanner.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writing unit emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
The optical writing unit, that is, an optical scanner that scans the charged surface of the image carrier with a light beam, used in such image forming apparatuses includes various optical elements (e.g., reflecting mirrors) and supports that support the optical elements. However, such optical elements and supports may suffer from warpage due to machining and assembly errors during manufacturing and thermal deformation due to heat generated by a motor during operation. When the light beam is reflected by a warped reflecting mirror, it may not scan the charged surface of the image carrier straight in a main scanning direction but instead may trace a curve along the surface of the image carrier.
To address this problem, the optical writing unit may employ a curve correction mechanism that corrects the curve of the light beam scanning the image carrier by correcting a direction and degree of curvature of the reflecting mirror. In this case, for example, the reflecting mirror is biased by plate springs attached to a non-mirror face disposed back-to-back to a mirror-face of the reflecting mirror that reflects the light beam at lateral ends of the reflecting mirror in a longitudinal direction thereof, respectively; the plate springs pull the lateral ends of the reflecting mirror inward to curve a center portion of the mirror face of the reflecting mirror into an inwardly concave shape. At the same time, the reflecting mirror is biased by a presser disposed opposite the non-mirror face of the reflecting mirror at a center of the reflecting mirror in the longitudinal direction thereof; the presser presses against the center of the reflecting mirror to curve the center portion of the mirror face of the reflecting mirror into an outwardly convex shape.
However, such configuration has a drawback in that the plate springs pulling the lateral ends of the reflecting mirror and the presser pushing the center of the reflecting mirror together deform the reflecting mirror into an uneven, wave-like form. Accordingly, a light beam reflected by the wave-like form reflecting mirror, when it scans the surface of the image carrier, itself traces a wave-like form optical path thereon, resulting in formation of a faulty electrostatic latent image on the image carrier.
To address this problem, the optical writing unit may employ two pairs of plate springs that slide over the reflecting mirror. For example, each of the two pairs of plate springs sandwiches the reflecting mirror via a holder mounted with two protrusions corresponding to the two pairs of plate springs. As the two pairs of plate springs move outboard from the protrusions, respectively, the center portion of the mirror face of the reflecting mirror in the longitudinal direction thereof is curved into a convex shape. By contrast, as the two pairs of plate springs move inboard from the protrusions toward the center of the reflecting mirror, respectively, the center portion of the mirror face of the reflecting mirror is curved into a concave shape.
However, such configuration also has a drawback in that the two pairs of plate springs sliding over the reflecting mirror, although they slide over a non-illumination section of the reflecting mirror not illuminated by the light beam, may peel off a surface vapor-deposited film of the reflecting mirror. Once the vapor-deposited film is peeled off the reflecting mirror, cracks may propagate in the vapor-deposited film from the peeled-off non-illumination section to an illumination section of the reflecting mirror that reflects the incident light beam, resulting in faulty reflection of the light beam and thus writing of a faulty electrostatic latent image on the image carrier.